OnePurpose and requirements of the experiment
1. Understand the phenomenon and process of coagulation and sedimentation, the role of water purification and the main factors affecting coagulation
2. Learn the basic methods of finding the best coagulation conditions for sewage (including dosage amount, pH value, and water flow velocity gradient).
IIMethodological principle
Colloidal particles have a certain charge, and the electric repulsion between them is the main factor in the stability of colloids. The charge value on the surface of the colloid is often expressed as the electromotive potential, also known as the zeta potential. The level of zeta potential determines the magnitude and range of repulsion between colloidal particles. Generally, the zeta potential of colloidal particles in natural water is about -30mv or more, and after adding coagulant, as long as the potential is reduced to about -15mv, a better coagulation effect can be obtained. Conversely, when the zeta potential drops to zero, it is often not the optimal coagulation state.
The amount of coagulant added directly affects the coagulation effect. Water quality is variable, and the optimal dosage varies and must be determined experimentally.
After adding coagulants such as A12(SO4)3 and FeCl3 to water, the destabilization effect of the generated AI(LIL) and Fe(III) compounds on colloids is not only affected by the dosage, the concentration of colloidal particles in the water, and the water temperature, but also by the pH value of the water. If the pH value is too low (less than 4), the hydrolysis of the coagulant is limited, and few polymer substances are present in its compounds, and the flocculation is poor. If the pH value is too high (greater than 9-10), they will dissolve, forming negatively charged complexed ions, and they will not be able to perform a good flocculation effect.
In the water with coagulant, the colloidal particles destabilize and coalesce with each other and gradually become large flocs, and the size of the water velocity gradient g plays a major role.
Experimental Procedure
The experiment was divided into three parts: the optimal dosage, the optimal pH value, and the optimal water velocity gradient. When the optimal dosage experiment is carried out, a stirring speed change mode and pH value are selected to find the optimal dosage. Then the optimal pH value of coagulation was obtained according to the optimal dosage. Finally, according to the optimal dosage and pH value, the optimal velocity gradient was obtained.
1) Experimental procedures for optimal dosage.
1. Use 6 1000ml beakers, put 1000ml of raw water respectively, and place them on the experimental mixer platform
2. Determine the characteristics of raw water, that is, measure the turbidity, pH value and temperature of the raw water sample.
3. Determine the minimum coagulation dose used to form alum flowers. The method is to slowly stir 200ml of raw water in the beaker and increase the amount of coagulant by 1ml each time until alum flowers appear. At this time, the coagulation dose is used as the minimum dosage for the formation of alum flowers;
4. Determine the amount of coagulant added during the experiment. According to the minimum coagulant dosage of forming alum flower obtained in step 3, take its 1 3 as the coagulant dosage of No. 1 beaker, take 2 times as the coagulant dosage of No. 6 beaker, find the coagulant dosage of No. 2-5 beaker by increasing the amount of coagulant dosage sequentially, and add coagulant to No. 1-6 beaker respectively;
For the oily wastewater of this experiment FTU=, coagulants (1.) can be added separately5）、（3）、（5）、（7）、（10）、（14）ml。
5. Start the mixer, stir quickly for one and a half minutes at 200rpm, and stir slowly for 10 minutes at 50rpm. The above stirring speed can be appropriately adjusted according to the nature of the raw water;
6. Turn off the mixer, let the precipitation stand for 15min, use a 50ml injection tube to extract the supernatant in the beaker (about 100ml in total) and put it into the 200ml beaker, immediately measure the turbidity with a turbidity meter (each cup of water sample is measured three times), and record the measurement results.
b) Optimal pH protocol.
1. Use 6 1000ml beakers, put 1000ml of raw water respectively, and place them on the experimental mixer platform
2. Determine the characteristics of raw water, that is, measure the turbidity, pH value and temperature of the raw water sample. The raw water used in this experiment is the same as the optimal dosage test
3. Adjust the pH value of the raw water so that the pH value of the water sample from 1 to 6 beakers is equal to (pay attention to stirring evenly).
4. Add the same dose of coagulant to each beaker with a pipette (the dosage is determined according to the optimal dosage obtained in the optimal dosage experiment).
5. Start the mixer, stir quickly for one and a half minutes at 200rpm, and stir slowly for 10 minutes at 50rpm.
6. Turn off the mixer, let the precipitation stand for 15min, use a 50ml injection tube to extract the supernatant in the beaker (about 100ml in total) and put it into the 200ml beaker, immediately measure the turbidity with a turbidity meter (each cup of water sample is measured three times), and record the measurement results.
3) Experimental procedure for optimal velocity gradient in the coagulation stage.
1. According to the optimal coagulation pH value and dosage amount obtained by the best pH value test and the best dosing amount test, the same dose of HCl (or NaOH) and coagulant were added to 6 beakers filled with 1000ml of water samples respectively, and placed on the mixer platform
2. Start the mixer and stir quickly for one minute at 300rpm. Immediately, the water samples in No. 1-6 beakers were stirred at 30 rpm, 60 rpm, 90 rpm, 120 rpm, 150 rpm and 180 rpm for 10 min
3. Turn off the mixer, let the precipitation stand for 15min, use a 50ml injection tube to extract the supernatant in the beaker (about 100ml in total) and put it into the 200ml beaker, immediately measure the turbidity with a turbidity meter (each cup of water sample is measured three times), and record the measurement results
4. Measure the size of the stirring paddle.